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H.G.P.'s Avatar
 
Join Date: Apr 2002
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Piston Crown de-carbing...How much carbon is too much carbon?

Shown are my six pistons crowns de-carbed (stayed away from ring-land).

However, piston number 4 was so heavily carbed, that the top was "speckled marbled." So in removing the carb off that piston (shown second pic below), the number and letter on the crown is no longer visible. Would it be best to use a back-up piston to replace this piston, instead of this piston? (side skirt is fine on all pistons)

Also, do the opposite sides (underneath") need to be decarbed also?

Thanks


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1969 911 E Coupe
"Little Bull" "Horse"
"H." Heart, "G." Gears, and "P" the Porsche
Old 12-03-2004, 06:24 PM
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If you look at the end of the thread in my sig you can see how clean I got my pistons.

I am a little OCD when it comes to my stuff so you are probably just fine.

As long as your pistons still all weigh within a gram or two of the others there is no damage done by being a little overly abrasive with your piston domes.
Old 12-03-2004, 07:24 PM
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Quote:
Originally posted by 350HP930
If you look at the end of the thread in my sig you can see how clean I got my pistons.

I am a little OCD when it comes to my stuff so you are probably just fine.

As long as your pistons still all weigh within a gram or two of the others there is no damage done by being a little overly abrasive with your piston domes.
Thanks Tony, the weight idea, if I can find a scale, is a great idea.

Those pistons on your thread look like they came right out of a plastic factory bag. I can't see my pistons ever getting that clean underneath. How did you get them that clean underneath?

When I get the time, I'm going to try to post pics of my heads, they are gorgeous, OEM direct from Stoddards.
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1969 911 E Coupe
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"H." Heart, "G." Gears, and "P" the Porsche
Old 12-03-2004, 08:21 PM
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I probably should have posted a before and after pic of the #4 piston. What I noticed before decarbing it, was that the carbon was on in two overlapping distinct black colored layers.

The top black carbon layer, overlapped part of the piston crown. But it was still fairly thick. When I removed this first layer, the second layer, while being removed, left parts of the crown speckled with normal crown color, and also with numerous somewhat deeper carbon speckles. These second layer carbon speckles were difficult to remove. It's smooth now to the touch, but I still cannot tell how even compared to the newer ones due to the slopping and curves of the dome and the valve relief areas.
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"H." Heart, "G." Gears, and "P" the Porsche
Old 12-03-2004, 08:55 PM
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